Warning: 'CLASS_NAME' doesn't have upper case alpha-numeric prefix
The part before _PT_ must be uppercase alphanumeric to suppress the message (no special characters).  You can use whatever for the part after it though.
You could rename your classes to :
ABC_PT_Gltf and ABC_PT_Fbx. The _PT_ part means it is a panel class so there is no need to write it again afterwards in my opinion.